Just got back from the UK, was learning to drive a Black5 on the NYMR had a great time. Would highly recommended it. Anyway while visiting the daughter in Slough we took the train into Paddington. That got me wondering, (1) are there trains that pass thru Paddington or is that the end of the line. (2) Just before Paddington we ran beside the underground line, is there anyplace on the underground that interchanges with the railroad. (3) How do they get underground trains from one line to another as they seem to be at different levels. Just wondering?
If i remember corectly the underground trains that you passed out side Paddington would have been Hamersmith and City line trains. They are not conected to Network Rail at Paddington but pass over the mainline on a flyover at Acton. The sub surface lines (Hamersmith and City, Met and Circle) all share tracks with each other in the centre of London but the tubes (Central, Bakerloo, Northern and Picadilly) are all operated in isolation and do not intersect with each other in service. There are junctions between them however at various locations to allow stock moves and civil enginers trains to run from line to line. At present all heavy rail services terminate at Paddington but a project is being considered to build “Crossrail”, a tunnel through London from Paddington to Liverpool Street to allow full size commuter trains to run from Reading to Colchester or something like that.
The underground interchanges many places with “mainline” railways in London. Some commuter trains use the same tracks as underground trains like trains out of Marlybone share track with the District line to Amersham for part of the way and the Bakerloo line to Harrow and Wealstone and the District line to Richmond shares with the North London line wich also hosts freight trains. There was once even more interchanges, most of them are towards the outer fringes of London.
Paddington still has the tunnel access but no track connection to the underground last I saw. In steam days trains did run thru Paddington from the main line West, now only the Underground Hammersmith line does.
Some lines may have no connection at all with the rest, I beleive Waterloo and City reaches the surface track by a crane.
You’re right about the Waterloo & City line cars having to be craned out to go to the works for overhauls. In the past there used to be an elevator which connected its tracks to the surface (Until privitisation the Waterloo & City line belonged to British Rail!). But the International Station now occupies the site of the elevator, so they now have to resort to craning. (On one occassion in the days of steam a loco fell down the elevator shaft and had to be cut up in situ!).
The Underground has enough interconnections that you could travel over the whole system, at least in one of the smaller tube trains. The milage numbering passes between lines at these points.
IIRC The line out to Heathrow airport was originally built as surface line, but now runs with tube stock. The platforms are at a compromise height.
The end of the line out to kew Gardens is shared with Southern Region main-line electric stock (which is 3-rail instead of 4-rail).
There are some wonderful track maps of the underground published.